Hot stepwise drawing of polybenzimidazole strand material with independent free-wheeling idler rolls

ABSTRACT

By using at least three independent, free-wheeling idler rolls, high speed hot drawing of orientable synthetic strand material such as polybenzimidazole yarn is accomplished in a more favorable and improved manner as stepwise drawing is permitted in each of the passes through the heating zone; the strand material being drawn wherever the yield point occurs, rather than at a predetermined location for a fixed amount which might not be optimum.

[ 51 Mar. 27, 1973 United States Patent 1 [191 Bohrer et al.

[541 nor STEPWISE DRAWING 0F References Cited UNITED STATES PATENTS POLYBENZIMIDAZOLE STRAND MATERIAL WITH INDEPENDENT FREE-WHEELING IDLER ROLLS [75] Inventors: Thomas Carl Bohrer,

2,807,863 Schenker...... 2,624,934 1/1953 Munson et a1 Charlotte, 2,767,435 10/1956 A11es.. NCJ George Franklin Ecker, Toms 3,441,640 4/1969 Santangelo River N J David Hsiao T 3,541,199 11/1970 Bohrer etal.. g 3,526,693 9/1970 Rulison et a1. Chen, Wilmington, Del.

[73] Assignee: Celanese Corporation, New York, Primary Examiner-Donald J. Arnold Assistant Examiner-James B. Lowe AttorneyThomas J. Morgan, Charles B. Harris and Kenneth E. Macklin 22 Filed:

I Nov. 10, 1970 Appl. No.: 88,462.

[ ABSTRACT By using at least three independent, free-wheeling idler rolls, high speed hot drawing of orientable Related US. Application Data [63] Continuation-impart of .Ser. No. 769,893, Oct. 23,

1968, abandoned.

synthetic strand material such as polybenzimidazole 264/290 H RZOMDIG- 73 yarn is accomplished in a more favorable and im- [52] US. Cl.

, proved manner as stepwise drawing is permitted in [51] Int. 17/02, D02 l/22 each of the passes through the heating zone, the [58] held of Search"'264/290 290 290 strand material being drawn wherever the yield point 264/1) 73; 28/72 R occurs, rather than at a predetermined location for a fixed amount which might not be optimum.

3 Claims, 3 Drawing Figures HOT STEPWISE DRAWING OF POLYBENZIMIDAZOLE STRAND MATERIAL WITH INDEPENDENT FREE- WHEELING IDLER ROLLS This is a continuation-in-part of application, Ser. No. 769,893, filed Oct. 23, 1968, now abandoned.

BACKGROUND OF THE INVENTION This invention relates to treating fibers, filaments, and yarns, hereinafter referred to generally as orientable synthetic strand material, and more particularly, relates to improved apparatus and process for hot drawing strand material produced from high molecular weight fiber-forming synthetic polymers.

A common practice in the manufacture of synthetic strand material is to subject the material to hot drawing operations, i.e., drawing at elevated temperatures, in order to obtain the necessary orientation and improve physical properties such as tensile strength.

This is usually done by feeding the strand material from a supply package to feed and draw rolls in series, the draw rolls having a greater peripheral speed than the feed rolls. The strand material is heated between the feed and draw rolls by passing it, for example, through a zone of radiant heat, over a heated plate or pin, or through heated liquids or vapors.

Further, to achieve the desired residence time in the heating zone; to ensure adequate improvement in tensile properties, and at the same time to minimize necessary work space, the strand material is normally passed back and forth through the heating zone a number of times about a pair of idler rolls, spaced across at least a portion of the heating zone, at opposite ends of the zone to function as guide and return members.

The conventional idler roll is a one-piece cylindrical or frustoconical roll or roller having one or more grooves formed about its circumference for guiding a corresponding number of strand portions. Whenever such a one piece idler roll is rotated the grooves travel, of course, at uniform, fixed ratio, peripheral speeds.

FIG. 1 can be used to illustrate a conventional drawing system by envisioning units 6 and 7 each to be a one piece idler roll, i.e., together they comprise a single idler roll pair. Strand material 1 from a supply bobbin 2 is wound around a feed roll 3 and its idler spacer a sufficient number of times to ensure against slippage and is conducted through a centering guide 4 and through the front of a heating zone 5. The strand exiting from the rear end of the heating zone makes a one-half wrap around the single-piece idler roll 6 and is then conducted back through the heating zone for a second pass.

Again, upon emerging at the front, the strand makes a one-half wrap around the other single-piece idler roll 7 and is again conducted back through the heating zone for a third pass.

In this manner, wraps are additionally added to this idler pair to bring the strand material up to a given temperature; to heat set the strand material; etc. Upon exiting from the furnace on the last pass, the strand goes through a centering guide 8 to draw roll 10 with its spacer idler and is then taken up onto a bobbin 11. Draw roll 10 is normally rotated at a higher peripheral speed than feed roll 3 in order to draw or stretch the heated strand material.

Assuming no slippage, the single-piece, heating zone idler rolls must of necessity rotate at the same peripheral speed and therefore strand drawing of any substantial magnitude can only be accomplished during the initial entry and final exiting passes through the heating zone.

Further, even when using a pair of frusto-conical idler rolls, drawing is limited to a fixed amount at fixed locations during passes other than the initial and final passes through the heating zone.

Moreover, as drawing speed is increased, a reduced retention time in the heating zone for the initial pass can result in the strand material not reaching the temperature necessary for drawing. This will shift substantially all of the drawing to the final pass through the heating zone as is illustrated in Example I.

Thus, due to certain minimum residence time requirements as well as minimum draw requirements, drawing speed or productivityis particularly limited when using the above described pair of one-piece idlers in systems needing four or more passes of the strand material through the heating zone. L

The above limitations and disadvantages of utilizing the conventional system of a pair of idler rolls are particularly apparent when high temperature resistant filaments or fibers are being drawn. For example, when certain polybenzimidazole fibers and particularly certain aromatic polybenzimidazole fibers are subjected to hot drawing operations where drawing conditions are not within certain critical ranges, the fibers foam and/or explode, resulting in a porous fiber product having relatively low tensile properties.

SUMMARY OF THE INVENTION Accordingly, a primary object of the present invention is to increase production capabilities in systems for hot drawing orientable synthetic strand material.

Another object of the present invention is to improve physical properties of orientable synthetic strand material while achieving high drawing speeds.

, Another object of the present invention is to increase maximum draw ratios while achieving improved stability of drawn material.

Other and further objects and advantages of the present invention will become apparent from the following more detailed description.

In accordance with the present invention, hot drawing of orientable synthetic strand material such as polybenzimidazole yarn is accomplished in a more favorable and improved manner as stepwise drawing is permitted in each of the passes through the heating zone, the strand material being drawn wherever the yield point occurs, rather than at a predetermined location for a fixed amount which might not be optimum. This is achieved by using at least three independent, free-wheeling heating zone idler rolls.

In one aspect of the invention, processes wherein orientable synthetic strand material is hot drawn by passing strand material in tension through a heating zone, and about a pair of rotatable guide-and-return In another aspect of the invention, apparatus is provided for hot drawing strand material which apparatus comprises strand supply means, strand take-up means, and first and second idler roll means for permitting simultaneously at least four passages of the strand material through the heating zone, said first and second idler roll means adapted to be spaced across at least a portion of the heating zone, at least one of said idler roll means comprising at least two independent freewheeling idler rolls, whereby strand drawing is allowed wherever the yield point occurs.

Other and further aspects of the present invention will become apparent from the following more detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a preferred form of the apparatus for carrying out the present invention;

FIG. 2 is a more detailed view of independent, wheeling idler rolls; and

FIG. 3 illustrates yet another embodiment of the invention wherein the heating zone comprises a heated drawing shoe or plate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates the present invention in a preferred embodiment. Strand material 1 from a supply bobbin 2 is wound around a feed roll and spacer idler roll 3 a sufficient number of times to ensure against slippage and is conducted through a centering guide 4 and through a muffle furnace 5. The strand exiting from the furnace makes a one-half wrap around an independent freewheeling grooved idler roll 6a and is then conducted back through the furnace for a second pass.

Again, upon emerging at the front of the furnace, the strand makes one-half wrap around an independent free-wheeling grooved idler roll 7a and is'again conducted back through the furnace for a third pass. The strand exiting from the third pass makes a one-half freewrap around on independent free-wheeling grooved idler roll 6b and is then conducted back through the furnace for a fourth pass. In this manner, at least four, preferably five or more, and as many as 50 or more passes may. advantageously be made in accordance with the present invention. Upon exiting from the furnace on the last pass, the strand goes through a centering guide 8 to draw roll 10 and its spacer idler and is then taken up onto a bobbin 11. Draw roll 10 is rotated at a higher peripheral speed than feed roll 3 in order to draw or stretch the heated strand material.

FIG. 2 shows in more detail exemplary idler roll means in accordance with the present invention, which means comprise a plurality of independent free-wheeling grooved idler rolls A through F mounted ona common supporting shaft 12 and adapted to rotate freely, i.e., not being power-driven, and independently of one another, l.e., not being geared or otherwise rigidly connected to each other. I

FIG. 3 shows another embodiment of the present invention similar to that shown in FIG. 1 except the means for supplying and maintaining a heating zone comprises a heated shoe 13. The strand material may also be heated by passing it over a heated pin or through heated liquids or vapors (not shown).

To be noted is that the idlers need not be closely spaced, for the actual stretching is believed to occur between successive idlers not on them, i.e., the stepwise drawing takes place in the heating zone between each consecutive idler, from the slowest accepting yarn from the supply .roll to the fastest which feeds the stretch roll. Each idler need only be of sufficient width to serve as a guide track for the yarn or fiber to be drawn and of course may possess a groove.

Moreover, means (not shown) for measuring and controlling the temperatures of the muffle furnace and the heated shoe shown in the drawings can also be utilized in the practice of the present invention.

Strand material which may be treated in accordance with the present invention includes filaments and yarns of fiber-forming polymers such .as, for example, the polybenzimidazoles, e.g., poly-2-2'-m-phenylene- 5,5- bibenzimidazole; the polyesters, e.g., polyethylene terephthalate; the polyolefins, e.g., polypropylene; the polyamides, e.g.,.polyhexamet'hylene adipamide; and the acrylics, e.g., polyacrylonitrile.

Using the above-mentioned polymers, filaments and yarns having a denier range, for example, of about 10 to 2,000, and preferably about 50 to 500, may be treated in accordance with the present invention.

Drawing of the above-mentioned strand material can be accomplished with the apparatus illustrated in FIG. 1 by rotating the feed roll 3 at a rate R and rotating the draw roll 10 at a rate R The resultingoverall draw ratio is R /R,. For example, polybenzimidazole fibers may be drawn at any desired draw ratio below that at which the fiber breaks, typically in the range of about 1.511 to 3.5: l and preferably from about 2.011 to 3.2: 1.

To achieve the desired improvement in physical properties, the strand material must have a sufficient residence time in the heating zone.

In general, residence time depends upon the strand material being treated and the temperatures in the heating zone.

For example, residence times of about 0.001 to 60 seconds may in general be adequate for the strand material described above. More specifically, residence times of about 5 to 20 seconds are normally sufficient for filaments and fibers of polybenzimidazole. Of course, larger yarns will generally require a longer residence time than smaller yarns.

The temperatures maintained in the heating zone should be high enough to allow the desired drawing and orientation of the strand material, but below that necessary to cause any significant degradation of the strand material. For example, temperatures in the range of about 300 to 700C., and preferably about 400 to 600C., would normally be adequate for polybenzimidazole filaments and fibers.

As stated, a significant advantage of the present invention is the capability of achieving high drawing speeds while attaining improved physical properties of the strand material. For example, drawing speed measured at the feed roll in the range of about to 300 m/min., or even higher, may be obtained without difficulty.

EXAMPLE I The stretching phenomena ina conventional hot drawing system was studied using a single one-piece free-wheeling idler roll at each end of a four foot muffle furnace to allow multiple yarn passes through the furnace, i.e., the yarn path went from a slowly driven feed roll; to multiple wraps around a single pair of freewheeling idler rolls; to a faster driven stretch roll: the multiple wraps traveling through a 500C. muffle furnace located between the idler rolls.

The strand material utilized was 12 dpf poly-2,2-(mphenylene)-5-5'- bibenzimidazole yarn. The polymer can be prepared in accordance with the methods described in US Pat. No. 3,174,947 and Re. 26,065. Yarn can be prepared from this polybenzimidazole by solution spinning using, for example, dimethyl acetamide solvent, in a manner known to the art. Results of this study are given below:

No. of Speed, m/min. Draw Ratios Passes Supply Stretch Idlers Total First Second 40 64 55.7 l.6 1.39 1.15 7 40 80 68.0 2.0 1.70 L18 7 40 96 80.5 2.4 2.01 1.19 11' 70 112 85 1.6 1.21 1.32 ll 70 I40 99 2.0 l.4l 1.42 ll 70 168 96 2.4 l.37 1.76

Total Draw Ration I draw ratio) X (2" draw ratio) The results show that two-stage drawing was occuring in the furnace, i.e., in the first pass in the furnace 1 EXAMPLE II A hot drawing system was examined as in Example I utilizing three independent, free-wheeling idler rolls;

two positioned at the entrance to the muffle furnace and one at the exit. The yarn from the supply roll passed through the furnace; made one-half wrap around the exit idler roll; passed back through the furnace and made one-half wrap around the No. 1 entrance idler. Five successive wraps were then made between these two idlers. On the fifth wrap around the exit idler, the yarn passed back through the furnace; made a one-half wrap around entrance idler No. 2; passed back through the furnace to the stretch roll and take-up. The results are as follows:

No. of Speed, m/min Passes Supply Idlers Stretch Exit Entrance Entrance No. I No. 2 12 224 224 231.5 250 i DRAW RATIOS Total Exit/Sp. No. 2/Exit St/No. 2 5 4.48 1.03 1.08

EXAMPLE III Using the conventional hot drawing system of Example I, i.e., a single pair of furnace idler rolls and the yarn of Example I, it proved impossible to produce a voidfree fiber at a supply feed rate of greater than 50 meters/min. therefore it was necessary to add a 2 foot preheater oven between the supply roll and the furnace. With this modified conventional system the following fiber physical properties were realized.

' Total Temp C. Supply Draw No. of TEN Elong Preheater Furnace Speed Ratio Passes g/d m/min 450 540 2.2 ll 5.48 23.3

MOD TE g/d 25.5 103 EXAMPLE IV Utilizing the three-idler system of Example II with the FBI yarn of Example I a significant improvement in the product physical properties was realized even without the use of the preheater oven.

SupplyTotal No. Furnace Speed Draw of TEN Elong MOD Temp.C. m/min Ratio Passes d girl 540 100 2.2 11 5.5 26 28 111 540 2.2 11 5.0 17 21 111 However, the properties began to drop as the input speed increased, as the above data shows.

EXAMPLE V The following example illustrates the preferred stepwise drawing manner in which the improved tensile properties with higher drawing speeds were obtained by the instant invention. The strand material is that of Example I. The apparatus used corresponds to that shown in FIG. 1, i.e., one independent free-wheeling idler roll per wrap as the yarn passes back and forth through the furnace, and the particular process conditions and properties obtained are given below. The mufflefumace used was 4 feet long as measured from the strand entrance to the strand exit.

SupplyTotal o. Furnace Speed Draw of TEN Elong MOD Temp.C. m/minRatio Passes g/d TE gld 540 100 2.2 5 5.4 24 26 94 540 150 2.2 5 5.3 22 25 111 540 200 2.2 5 6.1 19 27 123 As can be seen from the above, it is possible by the present invention to quadruple the drawing speed from 50 m/min to l 200 m/min and produce polybenzimidazole yarns having improved physical properties, e.g., tenacity values of five to 6 grams per denier or more and tensile factors (TE in excess of 25. The significance of the tensile factor TE is more fully discussed in an article by Dr. Arnold J. Rosenthal, TE An Index for Relating Fiber Tenacity and Elongation, Proceedings of the Symposium on Polypropylene Fibers, Sept., 1964, A Southern Research Institute Publication, Birmingham, Alabama.

Similar improvement in drawing speeds and physical properties may be achieved with filaments and fibers of other aromatic polybenzimidazoles such as poly- 2,2'(m-phenylene) 5,5'-bibenzimidazole; poly-2,2- (pyridylene-3",55,5'-bibenzimidazole; poly-2,2'-(furylene-2 ,5 )-5 ,5 '-bibenzimidazole;poly-2,2 (napthalene-l",6")-5,5-bibenzimidazole; poly-2,2- (biphenylene 4",4"')-5,5'-bibenzimidazole; poly-2,2-

amylene-5,5'-bibenzimidazole; ply-2,2'-octamethylene-S,5'-bibenzimidazole; poly-2,6-(m-phenylene)-diimidazobenzene; poly-2,2'-cyclohexenyl-5,5'- bibenzimidazole; poly-2,2',-(m-phenylene)-5,5'- di(benzimida-zole) ether; poly-2,2(m-phenylene)-5,5 -di(benzimidazole) sulfide; poly-2,2'(m-phenylene)- 5,5-di(benzimidazole)sulfone; poly-2,2'(m-phenylene)-5,5'-di(benzimidazole)methane; poly-2,2(mphenylene) -5,5" di(benzimidazole)propane-2,2; and poly-2',2"(m-phenylene)-5',5" di(benzimidazole)ethylene-1,2; as well as the other aforementioned synthetic strand materials.

The principle, preferred embodiments, and modes of operation of the present invention have been described inthe foregoing specification. The invention which is intended to be protected herein, however, may be practiced otherwise than is described without departing from the scope of the appended claims.

What is claimed is:

, l. A process for improving the tensile properties of polybenzimidazole strand material, which process comprises passing the strand material through a heating zone maintained at a temperature in the range of about 300 to 700 C., passing the strand material about at least three independent free-wheeling rotatable guide and return members to effect at least four passages of the strand material through the heating zone and to allow drawing wherever the yield point occurs, the total residence time in the heating zone of the strand material in the range of about 5 to 20 seconds, and taking up the strand material at a draw ratio of about 1.5:1 to 3.521.

2. The process of claim 1 wherein the strand speed as measured at the feed roll is above 100 m/min.

3. The process of claim 2 wherein the polybenzimidazole is poly-2,2'-meta-phenylene-5,S'- bibenzimidazole. 

2. The process of claim 1 wherein the strand speed as measured at the feed roll is above 100 m/min.
 3. The process of claim 2 wherein the polybenzimidazole is poly-2,2''-meta-phenylene-5,5''-bibenzimidazole. 